Morphological inspection method based on skeletonization

ABSTRACT

A morphological inspection method based on a comparison of real images—a real reference image and a real inspected image of an inspected object is disclosed.

FIELD OF THE INVENTION

The present invention relates to a morphological tracking method. Morespecifically, the present invention relates to an inspection method thatis useful in automatic inspection.

BACKGROUND OF THE INVENTION

Defects in the form of structural flaws, process residues, and externalcontamination occur during the production of objects such as PrintedCircuit Boards, semiconductor wafers, artwork or reticles. Defects aretypically detected by a class of instruments called defect scanners (orautomatic optical inspection systems). Such instruments automaticallyscan the object's surfaces and detect morphological or design anomaliesusing a variety of techniques. The location of these anomalies withrespect to the patterns on the object's surface is recorded. Thisinformation, or “defect map,” is stored in a computer file and sent to adefect review station.

Using the defect map to locate each defect, a human operator observeseach defect under a microscope and characterizes each defect accordingto type (e.g., particle, pit, scratch, or contaminant). Informationgained from this process is used to correct the source of defects, andthereby improve the efficiency and yield of the semiconductor productionprocess. Unfortunately, people are relatively slow and are quicklyfatigued by the highly-repetitive task of observing and characterizingdefects.

Methods of automatically characterizing defects, collectively known asAutomatic Defect Characterization (ADC) or Automatic Optical Inspection(AOI) have been developed to overcome the disadvantages of manual defectcharacterization.

One of the well-known algorithms that is used by AOI systems is askeleton comparison algorithm. This algorithm skeletonizes the objectsof both images—the reference image and the inspected image—and comparesthe skeletons' junctions and the skeletons' ends in both of the twoskeleton images. Skeletonization must be done in real time and in theinspection station. Moreover, the skeletonization process requires a lotof computing source. Consequently, the main disadvantage of theseinspection systems is that they are complicated and expensive.

It would be advantageous to have a method and a system, which onceskeletonize objects of a reference image and compare this skeletonizedimage with a real image of the inspected object. This method reducessignificantly the costs of the inspection scanners that intend to supplyonly a real image without real time sketetonization. Moreover, anothercomputer wherein the processing time is not very critical can do theprocess.

SUMMARY OF THE INVENTION

The present invention is a morphological inspection method based on acomparison of real images—a real reference image and a real inspectedimage of an inspected object.

According to the teachings of the present invention there is provided aninspection method based on a comparison of real images, made of thefollowing steps:

-   -   creating a reference mask that contains a first color image and        a second color image. The first-color image is obtained from        skeletonization of the reference real image, having a skeletons        image and the second-color image is obtained from        skeletonization of an inversion of the reference image, having        an edges-skeleton image;    -   painting the inspected image in a third color and performing        logical functions using the first-color image and the        third-color inspected image, having a first-defects-image, then        performing logical functions using the second-color image and        the third-color inspected image, having a second-defects-image;        and    -   combining the first-defects-image with the second-defects-image,        having a defects-image or defects-map.

By another aspect of the present invention it is provided the inspectionmethod, wherein at least one region-of-interest is defined, according toinspection criteria, in the reference image and in the inversion of thereference image—wherein the objects that are not inside the regions ofinterest are ignorable—and each of the skeletinizations ignore theignorable objects.

By yet another aspect of the present invention it is provided theinspection method, wherein skeletons of the first-color image and thesecond-color image are trimmed in a way that ignorable defects are notappearing in the defects-image or the defects-map when performing thelogical functions.

BRIEF DESCRIPTION OF THE FIGURES

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

In the figures:

FIG. 1 illustrates a mask preparation, according to the presentinvention.

FIG. 2 illustrates the inspection process.

FIG. 3 illustrates a flow chart of the method.

DETAILED DESCRIPTION

The present invention is a morphological inspection method based on acomparison of real images.

According to the method of the present invention, defining regions ofinterest on a first-color image of the inspection reference object. Thenon-defined regions are ignorable. Then, skeletonizing the image havinga first-color image. In the next step, inversing the inspectionreference object image and changing its color. Defining regions ofinterest and skeletonizing the image, having a second-color image of theobjects edges. The first-color image contains skeletons of the interestobjects, while the second-color image contains edges of the interestobjects.

In the inspection process, comparing a third-color image of theinspected object, with the first-color image. This comparison marks thedefects of objects' shape. Then, comparing the third-color image of theinspected object, with the second-color image. This comparison marks thedefects of objects' edges. By adding these two images, having a defectsimage.

The principles and operation of the method according to the presentinvention may be better understood with reference to the drawing and theaccompanying description.

Referring now to the drawing, FIG. 1 illustrates a mask preparation,according to the present invention. A first-color real image 11 is usedas a reference for inspection. The first-color image 11 contains objects13 for inspection and an ignorable object 14. Preferring an inverseimage 12, which is the inverse of the first-color image 11, but in asecond color. Identifying regions of interest 15 on both images 11 & 12and performing skeletonization on both images while ignoring ignorableobjects that are located out of the defined regions of interest. As aresult, having two images, a skeletons image (first color image) 16contains skeletons 19 of the interested objects and an edge-skeletonsimage (second color image) 17 contains skeletons 20 that are the edgesof the interested objects. The two images, the skeletons image 16 andthe edge-skeletons image 17, are used as a reference mask 18.

FIG. 2 illustrates the inspection process. The image 21 is the inspectedimage—obtained from an inspection scanner—contains interested imageswith a defect 23 a (disconnection) in one object and another defect 23 b(over-splay) in another object. In addition, the image contains anignorable object 24. The inspected image 21 is compared with thereference mask 18 first, by performing logical function using theinspected image 21 and the skeletons image 16 of the reference mask 18and second, by using the inspected image 21 with the edge-skeletonsimage 17 of the mask 18. As a result, having a defects image 22, whichcontains the first defect (disconnection) 22 a, which is recognized bythe skeletons-image 16 and a second defect (over-splay) 22 b, which isrecognized by the edges-skeleton image 18. Since non-interested objectsare not located in the regions of interest, the ignorable object 24 dosenot appears in the defects image 22.

FIG. 3 illustrates a flow chart of the method when inspecting an object.Transferring reference data (such as CAD data file or data achieved froma reference “golden” object) 25 of reference image 26 and inverting theimage into an inverse reference image 27, each in different colors.Marking regions of interest 28 in both images. Performingskeletonization of both images thus generating a defects image 35 ordefects file.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art,accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

1. A morphological inspection method based on a comparison of realimages—a real reference image and a real inspected image of aninspected—object said method comprising: a) creating a reference mask,said reference mask is comprised a first-color image and second-colorimage wherein: i) said first-color image is obtained fromskeletonization of said reference real image, thus generating askeletons image; and ii) said second-color image is obtained fromskeletonization of an inversion of said reference image, thus generatingan edges-skeletons image, wherein the reference mask, the first-colorimage and the second color image are created by a signal processor andare stored in a storage coupled to the digital signal processor; b)painting said inspected image in a third color and: (i) performinglogical functions using said first-color image and said third-colorinspected image, thus generating first-defects-image; and (ii)performing logical functions using said second-color image and saidthird-color inspected image, thus generating second-defects-image,wherein the first-color image and the second-color image are retrievedfrom said storage and wherein the painting and the performing logicalfunctions are performed by said signal processor; and c) combining bysaid signal processor said first-defects-image with saidsecond-defects-image, thus generating an inspection-defects-image ordefects-map.
 2. The method of claim 1, wherein at least one region ofinterest is defined, according to inspection criteria, in said referenceimage and in said inversion of said reference image—wherein objects thatexist outside of said regions of interest are ignorable—and each of saidskeletinizations ignores said ignorable objects.
 3. The method of claim1, wherein skeletons of said first-color image and said second-colorimage are trimmed in a way that ignorable defects do not appear in saiddefects-image or said defects-map when performing said logicalfunctions.
 4. The method of claim 1, wherein the performing of thelogical functions using said first-color image and said third-colorinspected image is independent of the second-color image.
 5. The methodof claim 1, wherein the performing of the logical functions using saidsecond-color image and said third-color inspected image is independentof the first-color image.
 6. The method of claim 1, wherein theperforming of the logical functions using said first-color image andsaid third-color inspected image substantially consist of applyinglogical addition to a region of said first-color image and to a regionof said third-color inspection image.
 7. The method of claim 1, whereinthe performing of the logical functions using said second-color imageand said third-color inspected image substantially consist of applyinglogical addition to a region of said second-color image and to a regionof said third-color inspection image.
 8. A morphological inspectionmethod based on a comparison of a real reference image and a realinspected image of an inspected object, said method comprising: (a)creating a reference mask that comprises a first-color image that is askeletons image and a second-color image that is an edges-skeletonsimage, wherein the reference mask, the first-color image and the secondcolor image are created by a signal processor and are stored in astorage coupled to the digital signal processor; (b) painting by saidsignal processor said inspected image in a third color; (c) applyinglogical functions to images of a group of images substantiallyconsisting of the first-color image and the third-color inspected image,to provide a first-defects-image, wherein the first-color image isretrieved from said storage and wherein the applying logical functionsare performed by said signal processor; and (d) applying logicalfunctions to a images of a group of images substantially consisting ofthe second-color image and the third-color inspected image, to provide asecond defects-image, wherein the second-color image is retrieved fromsaid storage and wherein the applying logical functions are performed bysaid signal processor.
 9. The method of claim 8, further comprisingcombining the first-defects-image and the second-defects-image, toprovide an inspection-defects-image.
 10. The method of claim 8, whereinthe creating comprises (i) skeletonizing the reference image to providea skeletons image; and (ii) skeletonizing an inversion of said referenceimage to provide an edges-skeletons image.
 11. The method of claim 8,wherein the applying of the logical functions to images of the group ofimages substantially consisting of the first-color image and thethird-color inspected image, substantially comprises applying logicaladdition to images of the group of images substantially consisting ofthe first-color image and the third-color inspected image.
 12. Themethod of claim 8, wherein the applying of the logical functions toimages of the group of images substantially consisting of thesecond-color image and the third-color inspected image, substantiallycomprises applying logical addition to images of the group of imagessubstantially consisting of the second-color image and the third-colorinspected image.
 13. The method of claim 8, wherein the two stages ofapplying the logical functions are carried out substantiallyconcurrently.